"I think we hold our relationships to a very high standard," she says."One of the most widely used justifications for cheating in America and Britain is: I wasn't happy'.
One important third reason that adultery is not such a common cause of divorce may be that couples can survive it better than they once could.
This may in fact be precisely because infidelity is common, an anticipated assault on a relationship rather than a death blow.
"People in rich countries risk a lot when they cheat: their marriages, their wealth, access to their children, plus, in some cases, the esteem of their family members and friends. "I discovered that married people in the West are pretty faithful.
They set monogamy as an ideal and by and large stick to it.
Thepicturein Scotland is even more dramatic: adultery ended 17% of marriages in 1981; in 2005 it was only responsible for 3% of divorces.
But that doesn't mean people are having less affairs than when Thatcher was in Number 10 and Sexual Healing was in the top 10.In 2005, there were 283,730 weddings in the UK, down 10% on 2004, and 155,052 divorces.In Scotland last year there were 13,013 divorces, an increase of 19% on 2005.In France and in Russia, an infidelity can be part of the story - not a necessary or a desired part, but certainly not a rupture." In fact, adultery is in decline as the legally given reason for divorce in the UK.In 1981, almost one in three divorces in England and Wales were granted on the grounds of adultery, but by 2005 that figure had fallen toaroundoneinfive.A BBC online poll from last year suggests that one in seven Brits have been unfaithful to their current partner, whether married or not, and the 2005 Global Sex Survey, conducted by Durex, found that 14% of British respondents had had an extra-marital affair.